Woven screen stretching frame

ABSTRACT

A frame for supporting and stretching a rectangular printing screen of woven material comprised of pairs of opposite frame members connected by and journaled within corner members at their ends. The frame members have means for gripping the screen material along each edge and are rotatable within the corner members to apply tension to the screen in either dimension to create the desired amount of stretch in it.

United States Patent [72] lnventor Wendell P. Dubbs 470 Nevada Ave.,Palo Alto, Calif. 94301 21 Appl. No. 770,595 [22] Filed Oct. 25, 1968[45] Patented Aug.3l, 1971 [54] WOVEN SCREEN STRETCHING FRAME 8 Claims,4Drawing Figs.

[52] us. C1 ,38/l02.91, 69/193,101/127.1,101/415.1 [51] Int. Cl D061:3/08, C14b 1/26 [50] Field ofSearch 101/127.l,128,128.1,415.1;69/19.1,19.3;.38/102.91, 102.4, l02.1,102,102.3,102.2,102.5-102.9; 24/2439, 243.10, 243.1 1

[ 56 References Cited UNITED STATES PATENTS 484,137 10/1892 Cauffield69/19.3 886,400 5/1908 Palmer 24/243 UX 988,331 4/1911 Greulich et a1.69/19.3 1,711,670 5/1929 Brennan 101/128.1UX 2,164,414 7/1939 Long24/243 UX Primary Examiner-Robert E. Pulfrey Assistant ExaminerC1iffordD. Crowder Attorney-Owen, Wickersham & Erickson ABSTRACT: A frame forsupporting and stretching a rectangular printing screen of wovenmaterial comprised of pairs of opposite frame members connected by andjournaled within corner members at their ends. The frame members havemeans for gripping the screen material along each edge and are rotatablewithin the corner members to apply tension to the screen in eitherdimension to create the desired amount of stretch in it.

PATENTEU M331 KQH FIG .4

INVENTOR, WENDELL P. DUBBS ATTORNEYS WOVEN SCREEN STRETCHING FRAME Thisinvention relates to improvements in woven screen printing apparatus andmore particularly it relates to a frame for applying the desired amountof tension to a woven screen after it is mounted on the frame.

In screen printing processes commonly known as silkscreening" a wovenscreen material is used and printing is accomplished by forcing inkthrough interstices of the screen provided by the weave or mesh of thescreen. The image to be printed is permanently formed on the screen byblocking certain of the interstices using a photo etching process or thelike. To achieve high quality results with good registration andresolution in silk-screening it is necessary for the screen to bemaintained stable and under tension so that when the ink is being forcedthrough it, the screen will not stretch. Hererofore, for high resolutionand precise registration a stainless steel mesh was required because ofits inherent resistance to stretching. However, such metal meshes wereextremely expensive. Also, they lacked durability since the small wiresforming the mesh were relatively fragile and tended to fracture, therebyrequiring the replacement of the entire screen. Other screen materialssuch as nylon were found to provide a similar quality of results if thescreen could be stretched to reduce the inherent resiliency of thematerial. Since nylon and other nonmetallic screen materials are muchless expensive than stainless steel it became important in the printingindustry to provide a mounting frame for a printing screen that canstretch a screen to any desired tension and retain it in that conditionduring its use. A general object of the present invention is to solvethis problem.

Another object of the present invention is to provide a frame formounting a sheet of mesh as woven material for use in a silk-screening"process that will enable an unlimited amount of stretch to be applied tothe sheet in either dimen-- sion. Thus, despite the characteristics ofthe sheet material used, most of its resiliency can be removed byinitial tension and the tension can be maintained over a long period ofuse.

Another object is to provide a frame for silk-screening on which theexact amount of stretch can be measured, thereby enabling successivescreens to be mounted thereon with ex-- actly the same amount oftension.

Still another object of my invention is to provide a frame for mountingand applying tension to a printing screen that is particularly welladapted for ease and economy of manufacture and can be supplied withvarious interchangeable parts to form frames of different sizes.

In general my frame is comprised of opposite pairs of rollerlike framemembers journaied in connecting corner members so that the frame memberscan be turned by a spanner wrench or some such tool and then be lockedin position. Each frame member has an axially extending means forgripping an edge portion of the screen, and increased tension on thesheet serves to increase the gripping force so no slippage can occur.Since each frame member is cylindrical in shape, it is inherentlystrong, and the entire frame structure can be light and easily handled.

Other objects, advantages and features of the present invention willbecome apparent from the following description presented with theaccompanying drawings, in which:

FIG. ii is a view in perspective of a frame embodying the principles ofthe present invention;

FIG. 2 is an enlarged fragmentary plan view in section taken along line2-2 of FIG. 1 at one comer of the frame;

FIG. 3 is a further enlarged fragmentary view in section of one framemember of the frame device in FIG. 1; and

FIG. 4 is a view similar to FIG. 3 of a modified form of frame memberfor my frame device.

Referring to the drawing, FIG. 1 shows a frame on which is mounted aprinting screen 112 for use in making so-called silk screen typereproductions. The frame is comprised of a pair of side members 14 ofequal length and end members 16 which may be shorter, all of which aresimilar in construction except for their length. Each frame member isgenerally cylindrical in shape and may thus be made from a metal tubingsuch as aluminum. At each corner of frame is a connector member 1% towhich one side member and end member are rotatably connected. Theseconnector members may be identical, each essentially comprising a rightangle member with integral flange portions extending from a junction atto each other. Fixed within each end of a frame member is a plug 20.Although various materials may be used for these plugs, I prefer to usea solid plastic having good bearing properties such as nylon. Each plughas a main body 22 which is press fitted into an end of the framemembers. An adjacent flange portion 24 has a diameter equal to that ofthe frame member and provides a bearing surface between it and theconnector member. A cylindrical boss portion 26 extends axially from theflange portion and fits; with a smooth running clearance within acylindrical hole 28 in the connector member.

From the outside surface of each tflange on the connector members is atightening screw 30 that extends through the hole b with its body 32being threaded into the plug 20. The screw is provided with a head 34having either a flat sided recess, as shown, or flat exterior sides tofacilitate its turning by an appropriate wrench. A washer 36 is providedbetween the screw head and the outer surface 38 of the connector flangeto increase the bearing area. Tightening of the screw 30 by a wrench onits head end draws the inner flange surface ii of the connector againstthe flange portion 24 of the plug and thereby prevents any rotation ofthe frame member after it has been rotated to its desired position. Whenthe screws are loose the frame members are rotated manually by means ofa suitable torque bar indicated by the numeral 42 in FIG. 1. The lattermay be attached substantially radially to the frame member as byinserting it in one of a plurality of spaced-apart radially extendingholes 43 which are circumferentially spaced apart near one end of eachframe member.

At the other end of each frame member! provide a series ofcircumferentially spaced-apart marks 4, and on the top edge of theadjacent connector flange or on the inner flange face 410 a single indexmark an is provided which can be aligned with themarlts M as the framemember is rotated. This enables the exact position of each frame memberto be ascertained and thereby enables the amount of frame memberrotation to be measured with precision so that a predetermined amount ofstretch can be applied to a particular screen.

In order for the screen material 12 to be stretched properly it must beattached to the frame members 14 and 116 along its edge portions so thatno slippage occurs even though the tension forces become substantial. Ascreen edge retaining means for each frame member essentially comprisesan external groove 48 extending axially along its length and providedwith an overhanging lip 50 along one side of the groove. In crosssection the groove is slightly V-shaped with bottom surfaces 52 thatslope inwardly and meet along a central low line. Within the groove 4bis an elongated retaining member M having approximately the same or aslightly narrower width as the groove and which is formed from someresiliently flexible.

material such as a suitable metal or plastic. Preferably, the retainingmember has a notch 56 that extends axially along its top surface so thatit will bend along a longitudinal axis to con form in cross section tothe shape of the groove when it is inserted therein. When the screen isattached to a frame member, its edge portion extends across and aroundthe overhanging lip portion 50, as shown in FIG. 3, and the frame memberis rotated counterclockwise. The tension created on the screen causesthe retaining member 52 to bind the edge portion of the screen moretightly in place against the overhanging lip. As tension increases inthe mesh 12, force is exerted perpendicular to the edge of the retainingmember M, which is restrained by an equal and opposite force from theedge of the groove 4%. These forces tend to further deform the member54, forcing it against the V-shaped bottom of the groove, with the mesh12 between, thereby automatically increasing the grip on the mesh astension is increased. Thus, the

edge portions of the screen are secured and no slippage can occur as theframe members are rotated.

In FIG. 3 one embodiment of a frame member is shown which may bemachined from common tubular metal stock. Adjacent the groove 48, a flatsurface 58 can be formed to which is connected an elongated rule member60 by means of a series of flat headed screws 62. The rule memberextends beyond the edge of the groove and forms the lip 50.

In the embodiment of FIG. 4, a modified frame member is shown which isformed as an extrusion with an integral lip member 50a overhanging agroove48a. A thickened portion 64 of the frame member extendslongitudinally below the groove to strengthen the frame member at thispoint and this also provides a locking lug which cooperates with a slot66 in the end plug 20 to help lock the plug in place and prevent anyrelative rotation with the frame member.

In use, the frame may be used for mounting a printing screen made fromany of a wide variety of materials. However, it is particularly valuablefor use with materials such as nylon which must be stretched to a pointnecessary to minimize resiliency. Once the edge portions of the screenare attached to the four frame members, the wrench 42 may be applied ina hole 43 to rotate each member the exact amount required, the amount ofstretch being measured by observing the number of calibration marks 44passing the index line 46.

When the desired degree of screen tension is reached the locking screwsin each corner connector can be easily taken up to hold the framemembers firmly in place. It can be readily seen that the operation of myframe is relatively simple, yet highly efficient. If frames of differentsizes are needed the same corner connectors can be used with pairs offrame members of different lengths. Thus, with one set of cornerconnectors and a stock of frame members, a printer can mount and use awide range of screen sizes.

To those skilled in the art to which this invention relates, manychanges in construction and widely differing embodiments andapplications of the invention will suggest themselves without departingfrom the spirit and scope of the invention. The disclosures and thedescription herein are purely illustrative and are not intended to be inany senselimiting.

I claim:

LA frame for supporting a printing screen comprising: a pair of endframe members and a pair of side frame members; means in each said framemember for retaining an edge portion of said'printing screen; cornerconnector means rotatably supporting each of said frame members at theirends to form a closed rectangle; and means for shifting said cornerconnector means along the axis of rotation of each of the adjacent framemembers and for locking said frame members against rotation after theyhave been rotated to a predetermined position. 2. The frame as describedin claim 1 wherein each said frame member is generally tubular and themeans'rotatably supporting each said frame member comprises a plug fixedwithin each end of each said frame member and journaled in said comerconnector means.

3. The frame as described in claim 2 wherein said locking meanscomprises a machine screw extending through a portion of said comerconnector means and axially into a said p 4 The frame as described inclaim 2 wherein each said plug is made from a solid plastic material andhas an integral end portion journaled in a said comer connector.

5. The frame as described in claim 1 wherein each said comer connectoris a structural member comprised of a pair of side members integrallyconnected at right angles to each other.

6. The frame as described in claim 1 wherein said means in each saidframe member for retaining an edge portion of said screen comprises anaxially extending slqt, means forming an overhanging lip along one axialside of said slot, and a flexible retainer strip in said slot forbinding the screen material against said overhanging lip when tension isapplied to the screen as the frame member is rotated.

7. The frame as described in claim 1 including a series of axiallyaligned indicating marks circumferentially spaced apart at one end ofeach said frame member, and an index mark on a said comer connectoradjacent to said indicating marks on a connected frame member.

8. A frame as described in claim 1 further including a series ofradially extending holes circumferentially spaced apart at one end ofeach frame for reception of a turning tool.

1. A frame for supporting a printing screen comprising: a pair of endframe members and a pair of side frame members; means in each said framemember for retaining an edge portion of said printing screen; cornerconnector means rotatably supporting each of said frame members at theirends to form a closed rectangle; and means for shifting said cornerconnector means along the axis of rotation of each of the adjacent framemembers and for locking said frame members against rotation after theyhave been rotated to a predetermined position.
 2. The frame as describedin claim 1 wherein each said frame member is generally tubular and themeans rotatably supporting each said frame member comprises a plug fixedwithin each end of each said frame member and journaled in said cornerconnector means.
 3. The frame as described in claim 2 wherein saidlocking means comprises a machine screw extending through a portion ofsaid corner connector means and axially into a said plug.
 4. The frameas described in claim 2 wherein each said plug is made from a solidplastic material and has an integral end portion journaled in a saidcorner connector.
 5. The frame as described in claim 1 wherein each saidcorner connector is a structural member comprised of a pair of sidemembers integrally connected at right angles to each other.
 6. The frameas described in claim 1 wherein said means in each said frame member forretaining an edge portion of said screen comprises an axially extendingslot, means forming an overhanging lip along one axial side of saidslot, and a flexible retainer strip in said slot for binding the screenmaterial against said overhanging lip when tension is applied to thescreen as the frame member is rotated.
 7. The frame as described inclaim 1 including a series of axially aligned indicating markscircumferentially spaced apart at one end of each said frame member, andan index mark on a said corner connector adjacent to said indicatingmarks on a connected frame member.
 8. A frame as described in claim 1further including a series of radially extending holes circumferentiallyspaced apart at one end of each frame for reception of a turning tool.